Control System Pulleys Need Love Too!

[old man emu]

Elsewhere I've mentioned that there has been a spate of reports of worn control cables in GA airplanes, and have suggested that you inspect those in your airplane. To those of you who have dived into the dark recesses of your airplane, did you happen to inspect your pulleys while you were there?

 

Sure signs that your pulleys haven't been looked at for yonks are painted over screws on inspection panels. Even if you know that the panels have come off at every periodic inspection, how do you know that it was the pulleys as well as the cables that were inspected? While replacing cables and pulleys is a job for an L2 or LAME (because it involves disconnecting primary flight controls), there is nothing to stop an owner from inspecting these items and if a problem is noted, reporting it to someone qualified to fix it.

 

Pulleys are meant to rotate a little to ease the direction change of cables. If they stick, then cables and the pulleys themselves will wear and may eventually fail. Most commonly, a pulley will stick because the grease inside the pulley's bearing begins to dry out and harden. As the grease dries, the pulley stops moving freely and its "working arc" gets shorter until it finally stops moving and the length of the arc gets towards zero. After the pulley stops rotating, any movement of the control cable will be on one spot, and the cable will start cutting into the groove of the pulley. As the cable cuts down into the pulley, the tension on the cable will lessen, making control systems sloppy.

 

What can an owner/pilot do to remedy the situation? The first thing to do find out which pulleys are stuck. This is a two person job. Have a helper move the cable by operating the stick, rudder pedals or whatever controls the cable while you watch each pulley in turn to see that there is movement. If you are doubtful about a pulley, hold it between your index finger and thumb and have your helper move the control, or try to rotate it yourself.

 

If a pulley is stuck the next step is to get it rotating again. A squirt of penetrating oil such as WD-40 or Mouse Milk will help to soften the grease. Work the pulley back and forth with your hand until it is moving freely. Don't go undoing anything. If the pulley is held in a bracket by a bolt that acts as an axle, then a properly operating pulley will rotate on the axle. A bit of penetrating oil on the axle can assist movement. If the pulley still doesn't come free, back out and call for your maintenance person to go further.

 

It is going to be normal to get wear in the groove of the pulley where the cable runs over it. In a properly operating pulley this wear spot will be an arc which is only part of the circumference of the groove. To get full life out of your pulley, just rotate the pulley 180 degrees so a fresh part of the groove is exposed to the pulley. I suppose you could just go 90 degrees and get four times the wear from one pulley.

 

While you are looking at the groove in your pulleys, you should be on the lookout for abnormal wear. If you spot it, call in the experts because abnormal wear is a sign of more extensive trouble than mere frozen bearings.

 

 

How often should you inspect your pulleys? The first inspection should be just before you close up the fuselage or wing during construction. Then it should be done at every periodic inspection, whether that be annually or for well used airplanes, every 100 hours. If you are building your own airplane, whack in inspection panels so you can access the pulleys. Make sure you add "Pulley Inspection" to your Schedule of Inspection.

 

Old Man Emu

 

 

[facthunter]

Good effort OME. We could do with more of this sort of thing. Nev

 

 

[old man emu]

ta

 

 

[cherk]

Good effort OME. We could do with more of this sort of thing. Nev

Well done OME ; terrific forum input....what about to the RAARag______sorry Mag?

Moving house ! uggh good luck and wish you the best for the holiday.

 

 

[old man emu]

What RAA Mag? This is the only real-time info source for Recreational Pilots!

 

OME

 

 

[naremman]

Great advice OME. We operate a 38 year old C172, and for the past decade have made a practice of lubricaticating the aileron cables and pulleys with generous lashings of ACF 50. I don't think there are too many aircraft that will ever drown from a surfeit of ACF 50, though it does have the disadvantage in a dusty environment in attracting nearly every dust particle.

 

There are some advantages of aircraft that rely me on torque tubes rather than cables!!

 

 

[old man emu]

We operate a 38 year old C172, and for the past decade have made a practice of lubricaticating the aileron cables and pulleys with generous lashings of ACF 50. I don't think there are too many aircraft that will ever drown from a surfeit of ACF 50, though it does have the disadvantage in a dusty environment in attracting nearly every dust particle.

WHOA!!!!!

 

Don't leave your cables and pulleys awash with lubricant! They are meant to run dry, and you've said that yours attract dust.

 

DUST = GRIT= ABRASIVE COMPOUND = PREMATURE WEARING = SHORTENED SERVICE LIFE

 

Only use a light weight lubricant, and use it sparingly. You don't want your cables slipping on the pulleys. There are design parameters which take into account some degree of friction between the cable and the pulley. Also too much oil might cause softening of the pulley material and lead to failure of the pulley.

 

Sometimes, if a little is good, a lot can be bad.

 

OME